A manipulator provided with the vision seam tracking system of the present invention can be employed in many processing applications including applying sealant, contour mapping and, in general, in any processing application requiring adaptive path control. For purposes of an exemplary showing, the invention will be taught in its application to seam welding.
Once a manipulator is taught a program, it will move along the programmed path with high repeatability. While this is satisfactory for many applications, others require adaptive path control. For example, in a welding operation, if the parts being joined are not uniform in seam or joint location by virtue of manufacturing tolerances, heat distortion, or the like, the manipulator will weld along its taught path, even though the seam may be located elsewhere.
In order to overcome this problem, and to broaden the applications in which manipulators can be used, prior art workers have devised a number of vision guided seam tracking systems. The teachings of U.S. Pat. Nos. 4,542,279 and 4,590,356 are exemplary of such systems. In general, the prior art approach has required the vision system to guide the manipulator. Because of the guidance requirement, constraints are put on the prior art systems. Furthermore, prior art systems generally require a constant relationship between the camera and the part, inhibiting orientation changes while tracking takes place.
As applications for vision-guided welding systems increase in complexity, more processing and interpretation of data are required. Prior art workers have attempted to maximize the processing capabilities of the vision guiding equipment. A major drawback to this approach, however, lies in the requirement for large amounts of manipulator information in order to make the necessary coordinate transformations and to control the entire weld process, resulting in communication and performance limitations. As a further problem, the large amounts of manipulator information must be processed in real time.
The present invention is based upon the concept of guiding the manipulator by means of the manipulator control and requiring of the vision system only data as to the position of the seam in camera coordinates. The present invention includes means for taking camera data in camera coordinates and transforming the camera coordinates to manipulator coordinates independently of orientation angles. Matrices are used which accommodate the attitudinal changes at the camera introduced by changes of the orientation angles. The manipulator control has access to and the capability of processing the large quantity of manipulator data (position, orientation, etc.) required to build the transformation matrices. The result is a vision seam tracking method and apparatus capable of compensating for dynamically varying orientation angles. The manipulator's orientation angles may be user programmed as required by the weld process to achieve desired attack and push/pull angles and the like, without degrading tracking performance. This capability allows the welding of many parts which could not be performed if the orientation angles had to remain fixed.